From the limited info I've found omline they seem to go for around $550+/- providing you can find one.
The xl305 seems to be regarded as one of the best models.



I found some convolution impulses here:

http://www.xs4all.nl/~fokkie/IR.htm#Masterroom

but I only have the waves convolution verb and it requires a proprietary impulse form. According to the site these are for altiverb.